Nerves of Posterior Triangle of Neck
Accessory Nerve (CN XI)
- Entry: Emerges from deep surface of SCM (after supplying it), pierces the investing fascia, and enters the posterior triangle at the junction of upper one-third and lower two-thirds of SCM
- Course: Runs obliquely downward and backward across the posterior triangle, lying on the floor (on levator scapulae), covered by investing fascia
- Exit: Passes deep to the anterior border of trapezius (approximately 5 cm above the clavicle) to supply it
- Relation: Accompanied by branches of C3 and C4 (proprioceptive to trapezius)
Mnemonic — Entry point: Nerve Point / Erb’s Point = junction of upper 1/3 and lower 2/3 of posterior border of SCM — site where all cutaneous cervical plexus branches emerge, and where CN XI crosses.
Cutaneous Branches of Cervical Plexus
All four cutaneous branches emerge at Erb’s point (nerve point of the neck) — junction of upper 1/3 and lower 2/3 of posterior border of SCM.
| Nerve | Root | Area Supplied |
|---|---|---|
| Lesser occipital | C2 | Scalp behind ear, upper part of auricle |
| Great auricular | C2, C3 | Skin over parotid, lower auricle, angle of jaw |
| Transverse cutaneous (anterior cutaneous) | C2, C3 | Anterior triangle of neck, front of neck |
| Supraclavicular (medial, intermediate, lateral) | C3, C4 | Skin over clavicle, shoulder, upper chest |
Mnemonic (GLASS) for scalp nerve supply includes Greater Occipital, Lesser Occipital, Auriculotemporal, Supratrochlear, Supraorbital — lesser occipital and great auricular originate from posterior triangle.
Brachial Plexus (Trunks)
The upper, middle, and lower trunks of the brachial plexus are visible in the lower part of the posterior triangle (subclavian triangle), emerging between scalenus anterior and scalenus medius.
- Upper trunk (C5 + C6): gives off suprascapular nerve and nerve to subclavius
- Nerve to serratus anterior (Long thoracic nerve, C5,6,7): Descends on the outer surface of serratus anterior (not strictly in the triangle but relevant — injury causes winging of scapula)
Other Nerves
- Dorsal scapular nerve (C5): Pierces scalenus medius, runs to levator scapulae and rhomboids
- Nerve to subclavius (C5, C6): From upper trunk, passes anterior to subclavian vessels
Posterior Triangle of Neck | Cervical Plexus — Formation and Branches | Accessory Nerve — Course in Posterior Triangle